The proposed specialized Center of Research in Osteoporosis is a broadly based multidisciplinary, shared facility research program that has as its central theme the improved understanding of the inter-relationship of hormones (estrogen, calcitonin) and physical stress (electrical and mechanical) in preserving and restoring bone mass. Loss of bone mass is a complex phenomenon involving hormonal changes, inadequate diet, lack of mechanical stimuli, and perhaps even lack of appropriate endogenous electrical potentials arising from bone itself. It seems reasonable to assume that a complete understanding of the basic underlying cause of osteoporosis will not be gained until the inter-relationship of the various hormonal changes and mechanical and electrical effects of estrogen and/or calcitonin deficiency on bone mass and relate this to the mechanical and electrical properties of bone at the molecular, cellular, osteonal, and whole bone levels. In each of the proposed projects the strategy is to try and relate hormonal, mechanical, or electrical effects, singularly or in combination, to osteoporosis. The four core facilities relate to this strategy in that they each provide two or more of the projects with mechanical testing of bone specimens (Mechanical Testing Core), histomorphometry of bone specimens (Histomorphometry Core), computation and data analysis (Computation Core), and administration of personnel, facilities, supplies, and services (Administration Core).